This invention relates to a housing for an electric motor or the like and method for forming the housing, and more specifically to a housing where the structure for securing the end shields to the housing sleeve allows for automated assembly without sacrifice of quality.
Electric motors, and particularly fractional horsepower motors, must be of quality construction to give long service, and yet must be made efficiently and at low cost. The alignment and positioning of the end shields relative to the sleeve are critical. The end shields must be parallel to each other, and perpendicular to the longitudinal axis of the sleeve. The spacing between the end shields must be accurate as typically the end shields provide the mounts for the rotor bearings. Misalignment or improper spacing of the end shields severely shortens the life of the motor.
The savings of labor and material are also crucial. This invention is specifically directed to a structure for accurately securing the end shields to the sleeve of a motor housing without the use of separate fasteners, and such that the assembly of these parts may be fully automatic.
There have been numerous techniques for securing end shields to the sleeve of a motor. These have included welding, the use of separate clips or fasteners, tie rods, and the like. However, such techniques have been either labor intensive, required extra parts or fasteners, or failed to provide accurate or secure mounting of the end shields to the sleeve.
There are known techniques for attaching the end shields and sleeve without the use of extra parts. One such technique is disclosed in Feiertag U.S. Pat. No. 2,701,318. With the Feiertag structure, the end shield is axially located by its engagement with the end of the sleeve. This means that the length of the sleeve must be exactly dimensioned, and the ends must be exactly parallel and perpendicular to the longitudinal axis of the sleeve, within reasonable tolerances, because the end shields are positioned by their engagement against the ends of the sleeve.
Mastrodonato U.S. Pat. Nos. 3,567,973 and 3,732,616 disclose structures where lances are formed near the edge of the sleeve and act to locate the end shield longitudinally therein. Segments adjacent slots are bent radially inwardly to hold the end shield axially in place. Notches 20 and portions 22 secure the end shield rotationally, relative to the sleeve. Hence, Mastrodonato uses separate means for securing the end shield axially and circumferentially, requiring additional manufacturing operations and material.
Schaffer U.S. Pat. No. 3,884,385 discloses notches at the ends of the sleeve and locating tabs at the edge of the end shield to locate the end shield circumferentially. Holding tabs formed at the edges of the sleeve hold the end shield axially. The formation of the locating tabs at the edges of the end shield requires extra material, and the holding tabs must be relatively thin so that they may be bent over against the locating tabs.
The end shield mounting structure and method of the present invention overcome the disadvantages of these prior techniques. Generally, in accordance with the invention, the sleeve is lanced near its ends to provide tabs that extend radially inwardly and have surfaces that define stops against which the end shields are positioned. These stops are spaced from the ends of the sleeve so that the end shields fit within the sleeve either flush with the ends or slightly inset therefrom. The tabs act to locate the end shields axially in one direction. Each end shield has circumferentially spaced recesses at its outer edge and in its outer surface. These recesses may be formed in a forming die or by staking. Also, the sleeve is staked near its ends to produce protrusions that extend radially inwardly and into the recesses of the end shields, with the end shields positioned against the tabs. These protrusions cooperate with the recesses to locate the end shields against movement in the opposite axial direction, and secure them against rotation relative to the sleeve.
The tabs are formed by lancing and can be very accurately positioned to ensure that the end shields are properly spaced and aligned. The recesses and protrusions are also accurately located and sized so that the protrusions firmly engage the outer edges of the recesses and securely lock the end shields in position against both axial and rotational movement relative to the sleeve.
Hence, this invention provides a very accurate and secure mounting of the end shields and sleeve, without the need for separate fasteners, and with minimal waste of material. The assembly may be performed using fully automated techniques with the protrusions formed after the end shield is positioned against the tabs. The invention also allows for repair of the motor after assembly by punching the protrusions back out to remove the end shield. Assembly produces minimal disturbance of prepainted surfaces to reduce assembly time and cost.
These and other objects and advantages of the invention are apparent from the description to follow .